I don't follow LMP3 much. As for GTE, see my above post. In addition to that, the score for the class in an individual series would vary based on how many of the different car types are present in the series.

Too many things are still up in the air with the new iteration of LMP1 to put it higher than GTE/GTLM at the moment.

The scales used here have somewhat different benchmarks when comparing IMSA and the WEC, ELMS, etc.

Pulling out the paved run-off at the Glen could make that one a 10. Pulling out the paved run-off and making it an enduro could make Road America a 10. Adding the P cars and making it an enduro could make VIR a 10.

It's hard to compare permanent road courses and street circuits, since the sets of parameters are different. As circuits, I prefer Long Beach and Belle Isle over Austin, but they are short races, and don't include all classes.

2)
LM P1 - no
LM P2 - no
DPi - no
LM P3 - no
LM GTE-PRO - no
LM GTE-AM - no
GT3 - N/A
Apart from the huge amount of cars in GT3, there are no other classes that can actually sustain a race with healthy double-figure entries on their own (maybe apart from LMP3). Multiclass or nothing, sportscar racing at high level has always been multiclass.

For Q1 - most of these series already exist. WEC, ELMS, IMSA, Le Mans Cup. The only one that doesn't is GTE as the top, but we do see that in IMSA GT only races and as a proof of concept it works. GT3 obviously has the entire SRO catalog proving it works.

For Q2 - Prototypes on track on their own car be quite dull. Might as well watch single seaters at that point. The big draw of prototype racing for me is multi-class as it adds something completely different to the mix. GT racing is a bit different because it can become big touring car races.

ELMS still have some special atmosphere, while AsLMS provides some teams and drivers. Nevertheless, sometimes it's too much racing going on and I think some series are interesting only to compete in or cheer for you relatives or friends, who are at the wheel.

I'm not a Drivers' Championship fan as it has to be a monoclass to get the really best of the best. So I do not understand the whole concept of LMP2 with different chassis and attention upon drivers rather that cars. The same goes to LMP3. No engineering evolution - no interest, as I have no friends who compete there.

Alright so now that we know the entry lists and more of the calendars and Alonso effect (if exists) and all that jazz, let me slightly modify the original questions - and this time I am also including IMSA and some other smaller things because everything here is kind of related

So I have the list of events/happenings right here. Put the following grade you think describes your interest for following (however it is you might do) the said events next to them

A = I cannot for the world to miss this, it's my life!
B = I'm plenty interested in this
C = I'm moderately interested in this
D = If I have time / particular mood I might follow it... or not, it doesn't really matter
F = I couldn't care less whether this event exists or not

So for example:
RD2. Sebring 12 Hours B

If you don't care about any of the events of series X you can just put F next to the series name and remove the events